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A network of pulsars around the Earth embedded in a background of gravitational waves coming from supermassive black hole binaries. Pulsar signals measured with an array of global radio telescopes are affected by gravitational waves and allow the origin of background noise to be investigated. Credit: C. Knox
The results of a comprehensive search for an ultra-low frequency gravitational wave background have been announced by an international team of astronomers including scientists from the Institute for Gravitational Wave Astronomy at the University of Birmingham.
These ripples on the scale of the light year, a consequence of Einstein’s general theory of relativity, permeate all space-time and could come from the merger of the most massive black holes in the Universe or from events shortly after the formation of the Universe in the Big Bang. . Scientists have been looking for definitive evidence for these signals for several decades.
the International Pulsar Synchronization Network (IPTA), joining the work of several astrophysical collaborations around the world, recently completed its gravitational wave research in their most recent official data release, known as Data Release 2 (DR2).
This dataset consists of precision timing data from 65 millisecond pulsars – stellar remnants that spin hundreds of times per second, scanning narrow beams of radio waves that appear as pulses due to rotation. – obtained by combining the independent datasets of the three founders of IPTA. members: The European Pulsar Timing Array (EPTA), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and the Parkes Pulsar Timing Array in Australia (PPTA).
These combined data reveal strong evidence of an ultra-low frequency signal detected by many pulsars in the combined data. The characteristics of this signal common to the pulsars are largely in agreement with those expected from a gravitational wave “background”.
The gravitational wave background is formed by numerous overlapping gravitational wave signals emitted by the cosmic population of supermassive binary black holes (i.e. two supermassive black holes orbiting one around each other and eventually merge) – similar to the background noise of many overlapping voices in a crowded space. room.
This result further reinforces the gradual emergence of similar signals that have been found in the individual datasets of participating pulsar timing collaborations over the past few years.
Professor Alberto Vecchio, director of the Institute for Gravitational Wave Astronomy at the University of Birmingham and member of EPTA, says: “The detection of gravitational waves from a population of massive black hole binaries or d ‘another cosmic source will give us unprecedented information. on how galaxies form and develop, or on the cosmological processes that take place in the emerging universe. A major international effort of the IPTA scale is needed to achieve this goal, and the next few years could bring us a golden age for these explorations of the universe. “
“This is a very exciting signal! Although we do not have definitive evidence yet, we may be starting to detect a background of gravitational waves,” says Dr Siyuan Chen, member of EPTA and de NANOGrav, and head of IPTA. Research and publication DR2.
PPTA’s Dr Boris Goncharov cautions about possible interpretations of these common signals: “We are also looking at what else this signal might be. For example, it could possibly result from noise present in the data of individual pulsars that poorly modeled in our analyzes.
To identify the background noise of gravitational waves as the origin of this ultra-low frequency signal, the IPTA must also detect the spatial correlations between the pulsars. This means that each pair of pulsars must respond in a very particular way to gravitational waves, depending on their separation on the sky.
These signature correlations between pairs of pulsars are the “smoking gun” for gravitational wave background detection. Without them, it is difficult to prove that another process is not responsible for the signal. Oddly enough, the first indication of a gravitational wave background would be a common signal like that seen in the IPTA DR2. Whether or not this spectrally similar ultra-low frequency signal correlates between pulsars according to theoretical predictions will be resolved with additional data collection, expanded arrays of monitored pulsars, and continued searches for longer and larger data sets.
Consistent signals like that recovered with the IPTA analysis have also been published in individual datasets newer than those used in the IPTA DR2, from each of the three founding collaborations. The IPTA DR2 analysis demonstrates the power of international combination giving strong evidence of a gravitational wave background over marginal or absent evidence from the constituent data sets. Additionally, new data from the MeerKAT Telescope and the Indian Pulsar Timing Array (InPTA), IPTA’s newest member, will further expand future datasets.
“The first clue of a gravitational wave background would be a signal like that seen in the IPTA DR2. Then, with more data, the signal will become more significant and show spatial correlations, at which point we will know that it This is a gravitational wave We are very excited to contribute several years of new data to IPTA for the first time, to help achieve gravitational wave background detection, ”said Dr Bhal Chandra Joshi, member of InPTA.
Given the latest results published by the individual groups who can now all clearly recover the common signal, IPTA is optimistic about what can be achieved when these are combined in the IPTA 3 data release. Work is already underway. ongoing on this new data release, which will include at a minimum updated data sets from the four PTAs that make up the IPTA. Analysis of the DR3 dataset is expected to be completed within the next few years.
Dr Maura McLaughlin of the NANOGrav Collaboration said: “If the signal we are seeing now is the first clue of a gravitational wave background, then based on our simulations we may have more precise measurements. spatial correlations necessary to conclusively identify the origin of the common signal in the near future. ”
Discover the secrets of ultra-low frequency gravitational waves
More information:
Second publication of data from the International Pulsar Timing Array: search for an isotropic gravitational wave background, Monthly notices from the Royal Astronomical Society (2021). Second publication of data from the International Pulsar Timing Array: search for an isotropic gravitational wave background,(2021). DOI: 10.1093 / mnras / stab3418
Provided by the University of Birmingham
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